Dilators have been used by the medical community for many years. Dilators are commonly used by physicians to enlarge an incision prior to the introduction of a larger catheter or to temporarily stiffen a catheter during insertion.
A preferred non-surgical method for inserting a catheter involves the use of the Seldinger technique which includes an access needle that is inserted into the patient's vein. A guidewire is then inserted through the needle and into the vein. The needle is then removed and a dilator is inserted over the guidewire. The dilator is inserted a short distance into the tissue to dilate the incision and the dilator is then removed and discarded. The catheter is then inserted into the vein in the desired location.
Many long-term catheters are made of either a semi-rigid material such as a polyurethane or a soft material such as a soft urethane or silicone rubber. Many polyurethane catheters are sufficiently rigid to be introduced into a patient's vein percutaneously without surgery. However, one of the difficulties with many rigid polyurethane catheters is that they may be incompatible with the human body when left in place for long periods of time. The silicone catheters may be left in place for longer periods of time than many of the polyurethane catheters without traumatic problems in most patients. However, one of the difficulties with silicone catheters is that the initial insertion of such catheters usually requires surgical intervention because the soft, pliable, elastic properties of the silicone which contribute to its compatibility with the human body are the same properties that make it difficult or impossible to insert the silicone catheter percutaneously into the vein of the patient.
Another insertion difficulty arises during the insertion of the dilator into the soft catheter and the subsequent insertion of the dilator into the incision. If the dilator is too soft, the user may have difficulty inserting the dilator into the catheter due to the frictional resistance encountered while inserting the dilator into the catheter. If the dilator is too rigid, the user may injure the blood vessel of the patient as the dilator and catheter are inserted into the incision. In the past, prior devices have attempted to overcome the problem of inserting a dilator into the catheter by providing a dilator having a diameter which is significantly less than the diameter of the lumen of the catheter. In addition to the reduced external diameter of the dilator, the inner diameter of the opening on the distal end of the catheter was also reduced so that pressure on the dilator when it is inserted into the catheter will cause the dilator to contact the distal end of the catheter and thereby push the catheter into the incision. If the contact between the dilator and distal end of the catheter were not present, the insertion force by the dilator may cause the catheter body to expand against the incision and slide along the dilator, thereby preventing the catheter from sliding through the incision. Additionally, if the transition between the outer diameter of the dilator and the distal end of the catheter were not a smooth transition, there is an increased likelihood that the tissue will be torn rather than dilated by the catheter.
In one currently available hemodialysis catheter combination sold by Medical Components, Inc., of Harleysville, Pa., U.S.A., a silicone double lumen catheter is used with an inner Teflon.RTM. stylet. The Teflon.RTM. stylet is used to increase the stiffness of the catheter as the combination is inserted into the patient. The stylet is then removed from the catheter once the catheter is inserted into the patient.
A further problem created by the use of the reduced diameter opening on the distal end on the catheter is that the reduced diameter opening restricts the amount of fluid which may flow through the lumen of the catheter. This may create a lower flow area at the transition between the lumen of the catheter and the distal opening if further openings are present in the lumen. This may result in an increased likelihood of clotting in this flow transition area because the flow may be diverted to the side openings in the lumen rather than through the distal opening.
In the preferred form of the present invention a wire stiffener is provided. The wire stiffener provides many of the advantages of a conventional dilator while eliminating the disadvantages of a conventional dilator. The wire stiffener of the preferred embodiment is inserted into the catheter prior to the insertion of the wire stiffener and catheter combination over the guidewire and into the incision.
An alternate embodiment of the present invention overcomes the foregoing disadvantages of a conventional dilator by providing a stiffening wire which is initially inserted into the dilator to assist in the placement of the dilator into the catheter.